The enzyme superoxide dismutase catalyzes the conversion of superoxide into oxygen and hydrogen peroxide according to equation (1) (this process is often referred to herein and in the art as dismutation).2O2−+2H+→O2O2 
Reactive oxygen metabolites derived from superoxide have been demonstrated to contribute to the tissue pathology in a number of inflammatory diseases and disorders, such as reperfusion injury to the ischemic myocardium, inflammatory bowel disease, rheumatoid arthritis, osteoarthritis, atherosclerosis, hypertension, metastasis, psoriasis, organ transplant rejections, radiation-induced injury, asthma, influenza, stroke, burns and trauma. See, for example, Simic, M. G., et al., Oxygen Radicals in Biology and Medicine, BASIC LIFE SCIENCES, Vol. 49, Plenum Press, New York and London, 1988; Weiss, J. Cell. Biochem., 1991 Suppl. 15C, 216 Abstract C110 (1991); Petkau, A., Cancer Treat. Rev. 13, 17 (1986); McCord, J. Free Radicals Biol. Med., 2, 307 (1986); and Bannister, J. V., et al., Crit. Rev. Biochem., 22, 111 (1987). In certain situations, cells are deficient in natural SOD activity; for example, this may occur as a result of heart attack, organ transplant, and even cancer: cancer cells are often deficient in SOD and can thus permit superoxide concentrations to rise and can cause injury to surrounding tissue.
It is also known that superoxide is involved in the breakdown of endothelium-derived vascular relaxing factor (EDRF), which has been identified as nitric oxide (NO), and that EDRF is protected from breakdown by superoxide dismutase. This suggests a central role for activated oxygen species derived from superoxide in the pathogenesis of hypertension, vasospasm, thrombosis and atherosclerosis. See, for example, Gryglewski, R. J. et al., “Superoxide Anion is Involved in the Breakdown of Endothelium-derived Vascular Relaxing Factor”, Nature, Vol. 320, pp. 454-56 (1986) and Palmer, R. M. J. et al., “Nitric Oxide Release Accounts for the Biological Activity of Endothelium Derived Relaxing Factor”, Nature, Vol. 327, pp. 523-526 (1987).
Clinical trials and animal studies with natural, recombinant and modified superoxide dismutase enzymes have been completed or are ongoing to demonstrate the therapeutic efficacy of reducing superoxide levels in the disease states noted above. However, numerous problems have arisen with the use of the enzymes as potential therapeutic agents, including lack of oral activity (a common problem with polypeptides), short half-lives in vivo, immunogenicity of nonhuman derived enzymes, and poor tissue distribution.
In an effort to overcome the problems associated with superoxide dismutase enzymes, several investigations have been made into the design of non-proteinaceous catalysts for the dismutation of superoxide, and their use in various superoxide-related ailments. One group of catalysts which has been shown to be nearly as effective catalysts as the native superoxide dismutase enzymes are the manganese and iron complexes of pentaazacyclopentadecane ligands, described in U.S. Pat. Nos. 5,610,293, 5,637,578, and 5,874,421. These ligands include a pentaazacyclopentadecane macrocycle with various substituents on the carbons of the macrocycle, or with cyclic or heterocyclic structures attached to the carbons of the macrocycle. Some of these complexes possess potent catalytic superoxide dismutating activity, and produce anti-inflammatory activity and prevent oxidative damage in vivo. In addition, these compounds, which are sometimes referred to as SOD mimetics, have been shown to possess analgesic activity and to reduce inflammation and edema in the rat-paw carrageenan hyperalgesia model, see, e.g., U.S. application Ser. No. 09/057,831. Exemplary compounds of this type include those shown in FIG. 1.